Soy and Breast Cancer: What is the Connection?

Whole food dietary soy sources such as tofu, edamame, tempeh, soy nuts, and soymilk are darlings of the plant-based, vegetarian and vegan food movements and have been staples of Asian cuisine for centuries. But not too long ago, breast cancer researchers were concerned about soy’s ability to mimic estrogen in the body, possibly increasing breast cancer risk. So what’s the verdict? Should we be eating soy or not?

Does Soy Increase Risk For Breast Cancer?

Fantastic news for plant-based foodies everywhere, the resounding answer is no, eating soy does not increase breast cancer risk, and in fact, soy reduces our risk of being diagnosed according to studies.

The important caveat to focus on, however, is that soy consumption should come from whole, organic when possible, food sources. Our bodies recognize nutrients in their natural forms better than highly processed nutrients, and therefore glean more benefit from such natural whole food nutrients. When foods are processed (and soy is no exception, including soy supplement products or processed soy as an additive in products), there can be components involved that hinder the proper utilization of nutrients by the body. These may include (but not be limited to) pesticides, additives, and preservatives, especially if a genetically-modified form of soy is in question.

Building on this standpoint, let’s focus on how breast cancer survivors can benefit from soy. A 2010 study of 5,042 female breast cancer survivors measured soy intake against 5-year mortality and recurrence rates. Women who consumed the lowest amount of soy had a 13.1% 5-year mortality rate and 5-year breast cancer recurrence rates were 13.0%. However, the women who consumed the most amount of soy only had 5-year mortality rates of 9.2% and recurrence rates of 8.9%. And these rates remained constant regardless of whether patients had been diagnosed with ER-positive breast cancer or whether or not they were treated with Tamoxifen.

While soy has recently been cloaked in an aura of skepticism, the truth remains that soy is certainly more beneficial than questionable for most folks and therefore most definitely worthwhile to explore as a potential weapon to carry in your arsenal against the risk of initial diagnosis or recurrence of breast cancer.

Soy, Phytoestrogens & Estrogen

So if soy is such a health food, why the concern about estrogen and breast cancer risk? The answer lies in how certain types of breast cancer operate. While there are several types of breast cancer, the most common cancer is ER-positive, or estrogen-receptor positive cancer, meaning that the amount of estrogen in the body will effect the growth rate of that cancer. Effective treatments for these types of cancers often involve limiting estrogen in the body to limit the spread and growth of the cancer.

Phytoestrogen, also called dietary estrogen, is a naturally occurring plant-derived compound that chemically looks a bit like estrogen. Phytoestrogens can be found in a large variety of common plant-based foods like soy, flaxseed, sesame seeds, oats, barley, beans, lentils, apples and carrots—virtually the Who’s Who of healthy foods. Yet up until very recently, the fear of researchers was that phytoestrogen would act similarly to estrogen in the body and help ER-positive breast cancers to grow.

The simple fact is that while similar, phytoestrogens are not estrogen and to date, studies have not shown that phytoestrogens increase breast cancer risk, mortality or recurrence.

Soy As Part of a Plant-Based Diet

A typical Western diet including red or processed meats, refined grains, sweets, alcohol, and high-fat dairy products, all which have been associated with increased cancer risk and higher rates of obesity, a cancer risk in its own right. On the other hand, plant-based diets include a higher intake of vegetables, fruits, whole grains, fish, poultry, and low-fat dairy products and have been shown to decrease cancer risk.

Soy has an important place in our diets, particularly in regard to the plant-based diet that many are choosing to embrace in an effort to transition away from consuming animal products in light of the wide range of benefits that the plant-based diet has shown to provide.

Soy is a versatile food staple that spans across a variety of food categories. Nutritionally, it contains whole food carbohydrate and lean protein, as well as a healthful fat profile. It also provides a hearty source of calcium when fortified.

When including soy, it is recommended to choose whole food, organic when possible, sources of soy such as tofu, tempeh, edamame, soy nuts, and soymilk. Supplements should be avoided as they have not been studied sufficiently. In fact, preliminary studies have shown that supplements do not offer the same protective benefit of whole food soy products.

As with all diet changes, it is important to discuss with your healthcare team whether there is any particular reason that soy should be omitted from your individual care plan. For those that currently enjoy or plan to enjoy more soy products, rest easy knowing you are improving your breast health and reducing your risk of breast cancer.